At the moment, I have 6 USB peripherals connected to the computer, a single reference GTX 780 (stock clocks), an i7-3770K ( stock clocks atm and voltage with turbo boost and voltage set to auto), an H100i with the 2 stock fans, 2x4GB 1600Mhz Corsair Vengeance Low Profile white RAM, one 120GB SSD, one 250GB SSD, one 1TB HDD, and CM Storm Stryker front panel connectors all connected, a Gigabyte Z77X-D3H motherboard, and like 4 LED case fans.

750w would be fine if you are doing light overclocking. Hell, I think you can run 650w on 780 sli. Someone correct me if I am wrong.
I would start looking into a beefier psu if you want to push the voltages and go for some big overclocks though.